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Misbehaving boiler
Posted by: Mark Drake (62.189.28.---)
Date: August 28, 2007 07:55AM

Hello everyone,

As I feel that it’s very important that we should all share as much information as possible, good or bad, I’ve had a recent experience that we may all benefit from…

I drive my 735 regularly, mostly to work and back – a round trip of just less that 40 miles – it turns a chore into a delight! So far I haven’t had any problems that I can’t deal with on the roadside – until last Friday that is…

On my return home in the evening, I noticed the burner note changing more and more. Thinking that the fuel jets may need a clean, I pulled into a convenient layby and set about the job. On opening the side flap to access the burners I was horrified to see a small dribble of water from one of the venturis and the pilot extinguished. Clearly some leaking tubes in the boiler. I have to admit that I was a little surprised as I have never scorched the boiler and treat it with great respect; always blowing down, regular washouts, that kind of thing.

I judged that although I could probably press on with the journey, I was losing water from the boiler and any hold up would probably force me to stop. I was also concerned that further leakage may crack the burner plate etc, etc, so I admitted defeat and got home courtesy of the RAC.

On dropping the burner the next day, I noticed a surprising amount of debris, mostly oxide flakes sitting in a heap on top of the burner plate. I have to admit that earlier in the season on inspecting the fire tubes, I noticed that the tubes around the pilot to be slightly sooty so gave the offending tubes a jolly good sweep out; about 200 tubes in the affected zone. I hadn’t considered the volume of material to be a problem – but maybe it was. To make matters worse, I hadn’t thoroughly cleaned the burner for over a year.

The debris had accumulated on the burner plate in an area about 5” or 6” diameter, effectively blanking this area. I suspect that there was then a ‘cold spot’ in the fire which may have lead to sufficient thermal differential in the lower tubeplate to cause leakage.

It’s possible that the debris stayed in the same area on the burner plate as a consequence of ‘Chladni patterns’. These are the patterns that sand, etc. will form on a flat plate if the plate is vibrated. My burner howls (a lot less than it did, thank goodness) at a fairly stable frequency, which may have caused the debris to build up the way it did.

Anyway, I’ve expanded the tubes that still ‘beaded’ under hydraulic test and it will hold 500 lbs on hydraulic OK now. Ran out of time to do a steam test though.

When I ran the burner off the car it howled really loudly, and by putting a steel rod on the burner plate when howling the vibrations I felt were most intense. The burner burns very unevenly, so I’m going to investigate in detail over the next few weeks.

Moral of the story – keep all parts of the burner scrupulously clean, if you sweep the tubes remove the burner first. Check that the burner is burning evenly and if you notice any change in tone, investigate it. A change in tone means that something has definitely changed.

I will keep you posted on my progress, I get married in 6 weeks time so steam car stuff may have to wait a while…

I hope that someone finds this useful!

Mark Drake

Re: Misbehaving boiler
Posted by: Mike Clark (
Date: August 28, 2007 05:00PM


What a pain! Thanks for passing on your experience.

My burner also gets quite sooty towards the front above the pilot. I put this down to the inevitable smokey pilot flame which results from reduced air induction by the pilot when the main burner is on full flame. Look at it when you next fire up. There was a lot of soot in the flue tubes when I cleaned it out for the boiler inspector - some were almost blocked. Little and often would seem to be the best cleaning option with the hope that the soot in small amounts might get blown away.


Re: Misbehaving boiler
Posted by: (
Date: August 29, 2007 06:53AM

Words of wisdom.
I too am discovering the delights of burner maintenance.
the thought of removing the burner pan fills me with dread, so Ibuilt an extension for my vacuum with an angled bit on the end, poked it thru the inspection hatch and done a "reasonable" job of cleaning debri from the plate.

I am hopeful this has done the trick, but I do realise eventually I will have to bite the bullet.


Re: Misbehaving boiler
Posted by: Jeff Theobald (Moderator)
Date: August 30, 2007 03:18AM

Hi Dave,

In my experience, you will need to drop that pan, it’s not as bad as you think! Messy yes, but can be done in 30 minutes max.

You will then be able to inspect things properly. Considering where and who you have around when steaming, this should be done anyway, you will then be able to check the fire plate and fittings, take the opportunity to put a 900psi squeeze on the boiler to make sure all is well, check boiler plate thickness with ultrasonic tester, or get your local boiler tester to help you out. At the very least remove a fitting to check the state of the plate, a good clean of everything, new fire cement as necessary, I use a trolley jack to raise the burner back into place, make sure a good seal is made between the burner and boiler.

I would say, even though this is your first time, so to speak, you will be able to complete the whole operation in a day, and it will pay dividends, you will know your car that much better, and a clean burner is the secret to good steaming.

Hope this helps, Jeff.

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